As played by Chris Hemsworth, Thor staggers about like some celestial beer monster.

By the glittering gates of Asgard, Kenneth Branagh's big-screen Thor is a rum old affair. Yes, this superhero epic comes complete with CGI monsters, cacophonous battles and a scene in which our musclebound hero stands out in the rain and wails "Waaaah!" at the heavens. But it also contains some broad, fish-out-of-water comedy, an odd couple romance and a scene in which Thor storms into a pet shop and calls for a horse. I watched from the gods, chuckling at the sheer, silly exuberance of it all.

Thor, according to Norse mythology, is the god of thunder, lightning and, intriguingly, oak trees as well. In the 1960s the deity found himself repackaged by Marvel Comics, which brought him down to earth and paired him off with a foxy young nurse, although Thor's sombre, bombastic persona ensured that he never quite chimed with the fans in the way, say, Spiderman did.

Now along comes Branagh's jokey riff on the comic-book version, played out under tie-dyed skies and swinging between small-town New Mexico and a gleaming, tinfoil Asgard that looks like Nordic night at Studio 54. If Marvel Studios figured that the director would bring a little Shakespearean gravitas to the proceedings then by God, they've got another think coming.

As played by Australian newcomer Chris Hemsworth, our protagonist swaggers about like some celestial beer monster. Cast out of Asgard by his exasperated father Odin (Anthony Hopkins), he crash-lands in the desert where he is promptly run over by Jane (Natalie Portman), an earnest young scientist. Suffice to say Thor is not enamoured of these new surroundings. "I'm the son of Odin!" he roars, hurling mugs of coffee to the floor and grappling with the medics who want to inject sedative into his buttocks. "No more smashing!" scolds Jane.

What Thor desires above all else, of course, is his mystical hammer of hammering. And he had better find it sharpish because, up above, heaven is already going to hell in a handcart, what with Odin on his sick bed and the duplicitous Loki (Tom Hiddleston) scheming to forge an alliance with the frost giants. Only when the hammer makes its reappearance can Thor be returned to his former glories. Clobbered, believed dead, he suddenly rears up on Main Street, with his billowing red cloak and big, dopey grin. "Oh. My. God," breathes Jane, and she is more right than she can ever know.

I'd hesitate to call this a good film, exactly. It's overlong and all over the place. The sets are tacky and the script is in spasms. Some of the supporting players (most notably a stricken Stellan Skarsgård) appear poignantly all at sea. But there's something weirdly charming about it just the same. Branagh has knocked his film together with a terrific, freewheeling gusto. It has its tongue in its cheek and the fun is infectious. For all of its flaws, Thor's never a bore.